altering voltage

[odecius]

Hello All,
I need some advice about a stompbox I was going to make.  For some reason it says it requires 15v.  Is there a way to change this to 9v without altering the sound quality or causing some other problem?  Thank you and have a nice day.

[5thumbs]

Hello All,
I need some advice about a stompbox I was going to make.  For some reason it says it requires 15v.  Is there a way to change this to 9v without altering the sound quality or causing some other problem?  Thank you and have a nice day.

Please provide a schematic or a link to the stompbox you're looking at building.  You might be able to lower (or raise) the voltage without major modification to the circuit, but we'll need to see what the circuit is (via schematic) before we can assist you further.

[Skruffyhound]

You need to give us more info to be able to help you, a link/schematic etc.
If it wants 15 volts it's probably not going to sound as good at 9 volts. Try searching under ; power supply/headroom.
If you just want it to be 9 volts because thats the standard power supply, you could consider adding a charge pump to the circuit which will bump it up to 15 volts, so you put 9v into the box and the circuit runs on 15v thanks to a little circuit trick. Search under charge pump for this.

Edit. Brett beat me to it, anyway here is a link to the charge pump, you just need the first section to get 17 volts which you can then limit down to 15v if necessary.

Good luck

[odecius]

I am unable to post it...because I only have it saved on my computer but it is not letting me copy and paste it.  there is no way for me to attach it either.  I could email it to you if you want, you can pm me your email address.

[petemoore]

   nothing didgital in there>?
  Probably won't hurt to expose it to a lower voltage.
  no opamps and caps rated at <25v [probably] in there
  Probably wont hurt to use two batteries to make 18v, and try that.
  caveats being that the unknowns mentioned matter, and I think I put enough probablies to allude to the possible risks...see what the ratings of the components are before applying a higher than usual or recomeended voltage to them, never exceed rated component voltage [add 10% for safety margin, or more].
  Exceptions:
  Some places in the circuit may use say 6v caps in a position that never sees >3v.
  Don't go by the voltage output printed on wallwarts, when measureing them unloaded, then loaded, there will be a higher voltage seen with no load, could be as much as 30% higher.
  And other stuff maybe, I don't see the schematic and can't forsee every scenario.
 

[Skruffyhound]

You need to upload the schem to either the gallery here or to a file share site, many use photobucket, for example, and then link to it in a post. Photobucket will give you a link that opens directly as a picture here. It is free and you will be able to figure it out in a few minutes.

[5thumbs]

Okies, the thread originator e-mailed me the schem, which I then posted to Photobucket.com so we can all enjoy it.


Observations regarding power requirements (after reading datasheets from http://www.datasheetarchive.com):

NOTE: I'm assuming 18V as the max you'll want to run the pedal at.  Many, but not all, of the components listed below will run at greater than +18V Vcc, so if you want to go higher than +18V Vcc, please read the datasheets.

1) TL071 is rated at max +/-18V Vcc, giving a max supply voltage of +36V, which means +18V Vcc single-supply should be fine.  No minimum Vcc rating given for TL071, but +/-5V was the minimum voltage in their published curves, so I'll assume that +5V is the minimum Vcc tested and published for the TL071.

2) Both the 33174 (quad op amp) and 33172 (dual op amp) will run from 18V to 4V Vcc.

3) The 7V regulator for the NE570 chip, 78L05 (a.k.a., LM78L05), fine from 18V to 7V Vcc.

4) The NE570 compandor, while being fed 7V on Pin 5, does have a Vcc connection on Pin 13.  This means that the NE570 must be able to take the higher or lower Vcc.  Higher is no problem as long as you stay under +24V Vcc.  The minimum Vcc for the NE570 chip is +6V Vcc.

5) Electrolytic capacitors C1, C2, C4, C6 (NP), C8, C10, C11, C12, C13, C14, C17 must all be rated at 36V or greater.  (If they're > 25V but <= 36V, you could run the pedal at +18V, but at some risk of overloading an electrolytic cap in a fault condition.  2:1 safety margin is usually prudent, so what's why 36V or greater rating is recommended on these caps.)  FWIW, if you just replace all of these caps that are 1μF or smaller with metal film caps, most of which I keep in stock are rated > 36V.  That would only leave C4, C8, C10, C11, C47 and C17 as electrolytic caps, of which they should all be rated >= 36V.

So in summary, you should be able to run this pedal anywhere from +7V to +18V Vcc single-supply, according to the datasheets.  Mind you, you might find that the pedal has positive or negative side effects when the pedal is run at different voltages, so testing will be important.  I'm guessing they told you that the circuit MUST run on +15V Vcc is likely due to the datasheet on the NE570 listing +15V Vcc in its 'typical circuit' diagram.

Hope that helps.  Good luck!

[odecius]

First off thank you everyone for your assistance with this.  Second...another question about it.  Do you think I could use an 18 volt transformer such as the one found here for the power?    http://www.frys.com/product/6148309

[soggybag]

Looks like something from Stompboxology. Looks like a Tremolo with two oscillators?

It also looks like the power supply is pretty basic. There is A voltage in and B which is 1/2 A. And, the 5v Regulator.

Not sure if this would work. If you have an adjustable power supply, you could connect it at the correct voltage and then turn it down. The voltage would scale across the system, except the 5v would stay constant. The 570 works fine at 9v. Internally it's op-amps use a 1.8v reference voltage so this part of the circuit wouldn't need much change.

Seems like the oscillators should work at 9v and 4.5v.